The Evolutionary Psychology of Human Sex and Gender

By Daniel Pouzzner, 2000-Apr-11/12

cyanobacteria: of asexual procreation

jaguar: of sexual procreation

Sexuality is an indispensable mechanism whereby biological
evolution bridged the immense gap between asexual/Lamarckian
unicellular organisms, and the now plainly preeminent humans. For
tens of millions of generations, the lineage leading to humanity has
been formed and continued exclusively by sexual procreation. The
precise microbiological mechanics of sexuality vary widely from
species to species, while the functional consequences - strictly
sexual procreation, in which each individual has precisely two
parents, each contributing roughly half of the individual's genome -
is absolutely conserved. This evidences the overwhelming evolutionary
pressure in favor of the sexual mechanism.

In this essay, I give an overview of the differences between the male
and female human phenotypes, concentrating on mental distinctions.
For a broad treatment of human brain structures and mental phenomena,
see The Symphonic Architecture of Mind,
also by this author.

The only universal genetic difference between a male human and a
female human is that the male has an additional chromosome, ``Y'', and
it is by far the smallest of all. This tiny minority of genetic
content is all that's necessary to toggle between a male and female
phenotype - and in fact most of the male-specific blueprint is not on
the Y chromosome at all, but only toggled by it.

Phenotypically, males and females share every organ - every muscle,
every bone, every viscus, and indeed every suborgan of the brain -
each serving the same function, interrelated to other organs in
precisely the same manner - with qualitative gender dimorphism in only
the tiny minority with exclusively procreative functions, and a small
fraction of the machinery of the brain, particularly certain portions
subserving emotion. Overall size - and certain proportions
(particularly hip dimensions, but also nuances of facial features,
relative neck size, and various other details) - are dimorphic, and
males obviously have more hair (particularly on the face), but males
and females otherwise look the same.

The basic evolutionary pressures on males and females are
identical. Without regard for gender, genes tend to flourish which
encode phenotypes that are successful in obtaining for themselves and
their relatives (those who share their genes - particularly children,
of course) healthy and regular supplies of water and foodstuffs, in
procreating, and in protecting themselves and their relatives from the
diseases and injuries that are caused by environmental elements,
microbial insults, from social or predator attack, or from accidents
and errors of action. This success has ample social dimensions, and
because humans are highly social, there is a definite - if modest -
gender dimorphism in the mechanical and mental aptitudes of males and
females. Nonetheless, these dimorphisms are quantitative differences.
Neither gender has anything approaching a monopoly on any qualitative
capability aside from the basic mechanics of procreation themselves
(impregnation vs. pregnancy and infant nutritional provision).

In particular, cognition and emotion are characterized by very little
dimorphism. It is far easier to enumerate the differences than the
similarities, and I will do this forthwith.

Female procreative organs implement the mechanics of pregnancy.
The activation of this system is expensive metabolically, and grossly
impedes the envelope of physical performance. This activation is,
however, prerequisite to survival of the species. Female procreative
organs are internal and substantially protected from the elements and
from injury. Male procreative organs, in contrast, are exceedingly
exposed, so that male fertility has an elevated sensitivity to
physical injuries that are symptomatic of non-competitiveness. Male
procreation does not usually involve any metabolic or physical
taxation beyond that incurred by the sex act.

Sexually mature females have mammary glands that are deleterious to
performance in locomotion, combat, and many other physical activities,
but permit the provision of nutrition (and immune system information)
to children, which is prerequisite to survival of the species.

On average, within any congenetic and ethnically homogeneous
sexually mature human sample space:

Females have a higher proportion of body fat, which is mildly
deleterious to locomotive and other types of physical performance, but
is conducive to survival in lean times and to successful metabolic
provision during pregnancy. At puberty, an average female adds
approximately 30 pounds of fat in the hip region, amounting to 80,000
calories used to fuel fetal development in the third trimester of
pregnancy.

The dimensions of the female pelvis deviate from those of the male
pelvis in a manner deleterious to locomotive performance, but
permitting successful childbirth.

Females have immensely less facial hair, reducing resistance to
injury, but increasing expressiveness (and therefore depth and
precision of psychological influence), and through visual resemblance
to children, increasing the prospect that others will protect
them.

Females are smaller, and have less musculature, than males. This
reduces metabolic load, in exchange for the reduction in locomotive
and other physical performance made inevitable and permissible by the
other dimorphic adaptations.

The female reproductive system cycles with a period approximating
that of the lunar cycle, purging itself in menstruation at the end of
each cycle, and being capable of initiating pregnancy for only 5 of
the 28 days (with the actual fertilization window lasting for only a
single day).

Females who reach menopause live longer than males who reach a
chronologically equal age - that is, absent trauma, women live longer
than men.

On average, males are distinctly superior at hurling rocks and spears
at targets. In fact, on average they are discernibly superior at the
pursuit of goals through direct action without a social intermediary.
A female on average has a corresponding advantage in using social
mechanisms (particularly, language) to lead another person to act in
pursuit of her goals. Though the dimorphism in tendency and
aptitude is definite, of course males nonetheless pursue goals through
social mechanisms, and females do so through direct action without a
social intermediary.

Famously, males tend to navigate spatially, while females tend to
navigate using landmarks. This has been accounted for by reference to
the stereotypical role of the male as journeying hunter and the female
as homebody managing the inventory of household implements, but of
course this tendency is far from a hard and fast rule, and so does not
in fact evidence a strict compartmentation of roles along those
lines.

Males, because of their physical prowess and since they are not
weighed down by pregnancy or children in tow, are clearly better
suited to hunting journeys and to combat. To be effective, these
enterprises require social organization and coordination, and in
particular require that people be related to each other in terms of
who coordinates whom - that is, be organized into social hierarchies.
Males thus have a dimorphic phylogenetic emotional predisposition to
accept and perform within these organizations, and part of this is a
predisposition to obedience and leadership. One consequence of these
predispositions is that, while a female tends to have an advantage in
leading another individual - her mate, in particular - a male tends to
have an advantage in leading many other individuals at once - a whole
community, for example.

On average, males have a higher density of neurons in cortex,
roughly 35000 more per square centimeter. This, in combination with
an average brain volume (for congenetic adults) 10-15% larger than the
average female brain volume, endows males with a higher information
storage and processing capacity. The pressures that led to this
dimorphism are clearly complicated. Salient among them are the
asymmetric advantage to males of detailed working knowledge of broad
expanses of geography and its concomitant fauna, for the purposes of
hunting and warfare. Also asymmetrically advantageous is detailed
knowledge of the position, role, attributes, and personal connections
of the great many other people in the community with whom hunting and
warfare operations must be coordinated. The cognitive demands of
courtship (discussed below) tend to be greater for males. Opposing
the pressure for a larger more energetic brain is the pressure for a
brain that is metabolically easier to maintain. It is selection for
metabolic maintainability that results in females being smaller than
males overall, their brains included.

Because the loss of a few males - even quite a few - often results
in no significant reduction in the number of the next generation, and
because for a male the procreative dividend of heroic excellence tends
to be immense, on average males exhibit less strategic conservatism
than females. If an able male were to engage in coldly rational risk
analysis, this is precisely the strategy he would pursue: the dividend
and expectation of success in a heroic pursuit is so huge that the
penalty and expectation of failure is overwhelmed.

Because the number of the next generation is mostly insensitive to
the number of males engaging directly in procreation in the current
generation, males are in fact instinctually more free to dedicate time
and energy to matters wholly divorced from their own direct
procreative prospects. Males are simply under less evolutionary
pressure to procreate successfully. A male is nearly as effective at
propagating his genes indirectly, by attending to the logistical and
strategic interests of his congenetic community, as by actually
procreating directly. In some cases this may even be more effective
than direct propagation. Upon close examination, it is my impression
that male homosexuality is a bona fide physiological condition in most
cases. This is quite congruous with the reduced evolutionary pressure
on males to procreate directly. In fact, it can be argued that the
incidence of male homosexuality is evidence of a selection for
community members who contribute only indirectly to the evolving
genetic corpus of the community.

This incidence is created in a particularly clever way. With each
subsequent pregnancy with a male fetus, the likelihood of a homosexual
phenotype increases by about a third. This may be because a woman tends to subject successive children to
increasing concentrations of testosterone in utero, which in utero has
feminizing effects (estrogen has masculinizing effects in utero).
Or it may be an effect of the mother's immune system activity.
Whatever the cause, with progressing probability, the male children of prodigious
mothers have an attenuated or wholly lacking instinct to procreate
(with a drive to engage in superficially similar acts remaining as a
largely inconsequential residue, venereal disease notwithstanding).
The particularly clever aspect of the mechanism is that it tends to
offset the mother's genetic over-representation, caused by a plethora
of male offspring, with effectively inhibiting distortion of the
procreative instinct.

In contests to win the favor of females, males pit themselves
against each other, and put on displays to demonstrate their fitness.
This activity is often dangerous, and consumes a great deal of time
and energy, which is therefore not available for directly constructive
efforts of immediate benefit to the community. Thus, reduced
participation among males in procreative competition, at the
individual level (as suggested in the previous paragraph) and in terms
of time invested (as discussed below, regarding menstrual synchrony)
is a collective adaptation. Of course, monogamy is the major
mechanism by which males and females alike avoid the perils of
procreative competition, and the modern free market system is the
major institution whereby competition among males is made to
constructively benefit the community instead of detracting from
it.

Construction and interpretation of sexually motivated behavioral
messages is highly dimorphic. Typically, a female offers noncommittal
clues, requiring careful decipherment, that lend themselves to easy
and plausible denial if her interest dissolves during courtship. She
requires that courtship endure for a lengthy period, sometimes many
months. A male, in contrast, readily and early offers explicit and
undeniable declarations and overtures, and prefers the shortest
possible courtship. The manner of interpretation is a mirror image of
this. The female ratifies only explicit and undeniable declarations
and overtures, and then only hesitantly and with the proviso that
economically expensive activity be displayed in clear support of the
declarations. She is largely oblivious to noncommittal clues. The
male is very sensitive to any conduct which might constitute a subtle
or covert declaration or overture, and tends to interpret and welcome
them as such, with little hesitancy or doubt. The female presents a
bevy of puzzles for the male to identify and solve, demonstrating his
prowess, whereas the female is loath to address any puzzle posed by
the male, who does not tend to present them in any case. The
rationale for these radically dimorphic adaptations is the radically
dimorphic level of risk and investment represented by the sex act.
The male stands to lose almost nothing by it, and so interprets even
the subtlest and most ambiguous of gestures as an overture to engage
in sex. He easily delivers dramatic and plain declarations and
overtures, since so little is at stake. In contrast, the female
potentially stands to lose everything, and so requires thorough,
undeniable, and consistent declarations of interest and commitment by
the male, clearly corroborated by his conduct. She delivers dramatic
and plain declarations and overtures, if at all, only after a lengthy
and exhaustive courtship has confirmed the viability of the male.

On average, the magnitude and incidence of jealousy is roughly
similar in males and females. However, its causes are distinctly
dimorphic. Male jealousy is usually prompted by a suspicion or
determination that a female partner is engaging in coitus with someone
else. Female jealousy usually follows from a suspicion or
determination that a partner's emotional fidelity has been diluted or
redirected by involvement with someone or something else - involvement
which needn't even be sexual. The explanation for the dimorphism is
clear: male procreative strategy centers on successful monopoly of a
female's procreative organs, whereas female procreative strategy is
the pursuit of a monopoly on the protective and productive attention
of a male partner.

Males have a tendency to specialize - to construct intensely
detailed cognitive models of, and direct intense attention at, a
particular narrow field of activity. Specialization is itself a risky
strategy, since a skillset can be rendered obsolete by cultural
innovations, but competitive excellence can be attained only by
specialization. (Importantly, an individual is not limited to a
single area of specialization.) Specialization is not about adequacy,
it is about excellence. A community without specialists is at a gross
competitive disadvantage compared to one that has them - this is why
division of labor is de rigueur in real world economic practice.

Indeed, competition is a far more natural theme for males than for
females. Cooperation is clearly a natural theme for both genders.

Motherhood is not in fact a specialty, and females are predisposed
to construct sweeping, generalistic, integrative world models,
suitable for presentation (to children, but also to other community
members) and enforcement (detecting when a rule has been broken, and
directing corrective action). That there is a phylogenetic
institution concerned with forming, relaying, and indeed imposing
integrative world models, is vital to cultural continuity and
consistency, and this continuity and consistency immensely benefits
survivability.

The menstrual cycles of women in prolonged proximity synchronize,
so that whole communities can achieve a synchrony in which procreation
exerts a major influence on community activities for only a week or so
each month. This adaptation has multiple dividends. The disruption
and destruction of procreative competition is confined, allowing the
community to concentrate on other matters most of the time. That
competition is also concentrated, so that the procreative prospects of
less fit males are made all the dimmer.

This synchrony also tends to inhibit the genetic uniformity and
potential for incest that would result if a single dominant male were
able to impregnate many or most women in his community by moving at a
leisurely pace from one to another. With the traffic jam of fertility
created by cyclical synchronization, he is simply unable to reach most
women before they have already been impregnated by other men who are
in regular and prolonged proximity to the women. Though it is hardly
prohibitive, the synchronization phenomenon is a phylogenetic pressure
toward monogamy or diversity, and against harem-like arrangements.

Human sperm is of a low quality - relative to many animals,
including primates, a low proportion of the sperm is viable - and this
encourages pair bonded sexual partnerships to the detriment of any
arrangement of irregular and infrequent coitus, particularly
harem-like arrangements and surreptitious affairs.

Women's visual and olfactory sexual preference is biased toward
desirable partners during the period of fertility and toward less
desirable ones the rest of the time. This is likely an adaptation
running counter to monogamy, which tends to maintain the procreative
availability of desirable partners and the pacification and
utilitarian engagement (household protection and production) of
undesirable ones. Underscoring this adaptation, incidence of orgasm
in females is predominantly dictated by the perceived sexual
(hereditary) desirability of the male, and household partnership or
emotional involvement is not a predictor. This is significant because
the vaginal and uterine contractions that accompany orgasm promote
successful fertilization. Exerting an opposite influence on the
probability of successful fertilization is ``flowback'', by which
unwanted semen is expelled from the vagina.

Human ovulation is concealed, not advertised. This is unusual
among extant species, and the development of this adaptation
underscores how vital it is to the evolution of the species that women
maintain substantial, practical, if largely unconscious control over
their impregnation.

The temporal window during which fertilization is possible ends
just 24 hours after ovulation. Only during this period, the uterine
mucosa drop their immunity-enhancing viscosity sufficiently to allow
penetration by sperm. Desired sperm that arrive prematurely are
waylayed and suspended in pockets in the cervical wall, and are
reanimated by a signalling mechanism when the fertilizable egg
makes its entrance. The pistonlike thrusting of the penis during
coitus, combined with the foreskin behind and under which debris is
accumulated, constitutes a pump that works to remove seminal matter
that might have been deposited by a sexual competitor. Additionally,
the duration since the male last engaged in coitus with the instant
partner modulates the volume of his ejaculation, to better the chance
that a competitor's attempt at fertilization will be thwarted by his
own.

Oral sex is a practical behavior. Through various sensory channels
- but primarily, through olfaction and taste - the one playing the
oral role is able to gain information revealing the health of a
present or prospective partner, and often, whether he or she has
recently engaged in sex with someone else.

Masturbation in males serves to purge the seminal tracts of sperm
that is no longer viable, and is perhaps useful in purging the system
of other perishable fluids. Male masturbation culminating in orgasm
(and concomitant ejaculation) is only possible with direct physical
manipulation. Masturbation in females serves no practical purpose,
and orgasm can be attained completely in the absence of direct
physical manipulation.

Female homosexuality is largely or entirely an unintended and
inconsequential result of the sexual drive. Exclusive homosexuality
(as distinguished from bisexuality) is pathological. Even among
exclusively homosexual females, maternal instincts tend to be very
much intact and overpowering. Insemination does not strictly
require the cooperation of the female, or in general require any
organized action by the female, so that the pressure to ingrain fixed
action patterns of procreation initiation is reduced relative to that
on males.

Rape is clearly disfavored. The positioning of the male genitalia
so that they are vulnerable to blows and injury clearly tends to
inhibit rape, though I think it unlikely that an adaptive selection
against rape accounts for the arrangement since the arrangement is
much older than bipedal mammals. The positioning of the female
genitalia so that insemination is impossible without separation of the
legs is also an arrangement that disfavors rape and is probably driven
partly by that dividend (lower animals have a similar arrangement by
way of a tail and the act of sitting). Flowback and concealed
ovulation, and some of the related mechanisms discussed above, also
strongly disfavor rape as a procreative strategy, and almost certainly
did develop precisely to this end. Rape is disfavored because
the strategic judgement of the female regarding when and with whom to
procreate has major immediate and long-term survival benefits.

Effective female procreative strategy is very different from
effective male strategy. There is a definite and not particularly
prodigious limit to the number of children a single female can
produce. Much more important to this analysis is the extreme cost and
risk involved in human pregnancy and childbirth (especially in the
pre-technological era during which humans evolved to their present
state), and the extreme cost of rearing a human - a cost that tends to
be asymmetrically borne by the birthing female. Females, particularly
those who are pregnant or have immature children, are thus extremely
risk-averse. For most, their inherent preference is a very orderly
and stable community that exchanges freedom for security, and less
reliable private resources for more reliable collective resources.
Moreover, this tendency to prefer security over freedom tends to be
proportional to the sexual attractiveness of the female, since the
risk of rape is otherwise similarly proportional. This theme
culminates in what Lionel Tiger (professor of anthropology at Rutgers)
terms ``bureaugamy'', in which women embrace the state as protector,
provider, and head of household. Bureaugamy is a hybrid of three
components: the insatiable female appetite for security, the
institution of unrestrained universal democracy, and Hegel's vaunted
bureaucracy, whose agents - in order to obtain for themselves
resources and importance - orchestrate the extortive predation of
resources from producers, the bribing of constituencies with those
resources, and the protection of constituencies from predation.

Female procreative strategy is like that of single-celled organisms
- steady, inexorable multiplication - and this phylogenetic
procreative strategy greatly colors their total phylogenetically
predetermined ethos. Evolution has not yet had an opportunity to
embed in the genome awareness that this strategy is disastrous when
pursued by a technological species. It is an inherent conflict in the
species that this strategy is phylogenetically predominant for
females, while the characteristics that lead to technological
innovation are phylogenetically predominant for males.

Consistent with this strategy of inexorable multiplication, females
prefer to procreate with males who are important, leading to the
dimorphic tendency of males to pursue importance. Importance comes in
two flavors: influence or control over many other people (elevation in
the social hierarchy), and predication of the welfare of many other
people on the success of the male at issue in his chosen vocation. In
the former case, the advantage is that the male is positioned to
exploit the resources of the community to increase procreative
success, and that the male bears genes that are conducive to elevation
in the social hierarchy. In the latter case, two distinct pressures
are at work. The first is similar to that which accounts for the
appeal of influential males: the family of a male on whom the
community relies can expect extraordinary graces and protection from
the community. From the point of view of the female, the male's
vocation is just a roundabout route to influence. The second pressure
is quite different. The perpetuation of genes that produce people
with aptitude for activities on which community prosperity is
predicated is vital to the community (in the next paragraph, a special
case of this dynamic is treated), and so is selected for - by
tailoring of female human nature - prima facie. To a certain
degree, this pressure is at work even in the female preference for
leadership per se, since a community organized coherently by an
effective leader is more competitive than one that is socially
disorganized or incoherent.

In a seeming paradox, females often choose to procreate with males
who have a phylogenetic predisposition to wreaking havoc on order and
stability - who are the sort one might expect to choose and succeed in
heroic pursuit. The explanation for this instinct is that, without
the perpetuation of genes that lead to such tendencies, the community
loses its capacity to accommodate crises (disorder and instability -
particularly, warfare and natural disasters) and so is at a gross
disadvantage relative to a population that has retained this capacity.
In fact, without this capacity, humanity might have already passed
into extinction. The iconoclast is despised for the disruption he
threatens or causes, until the day he is revered as a hero for saving
society from far graver disruption.

In a mirror to the seeming paradox of the previous paragraph, males
- many of whom have a phylogenetic predisposition to shattering order
and stability - often choose to procreate with females who are
risk-averse and hostile toward things that threaten order and
stability. The explanation is also a mirror - stabilizing and
preservative influences have great survival value - but more
obviously, these traits are precisely those that are conducive to
successful rearing of children.

It is well to mention some basic attributes, some dimorphic some
not, that play prominently in the perception of sexual desirability.
The waist to hip ratio preferred by average males in females is .65,
whereas that by average females in males is .85. These are the
average ratios seen in the population. Females prefer males with
proportionately larger necks, and males prefer females with
proportionately more slender necks. This is also observed in the
population. Other typical markers for the estrogen suffusion that
accompanies normal female puberty are a small chin, full lips, amply
proportioned breasts, and relatively prominent eyes, and these traits
are attractive to average males, though their adaptive value in and of
themselves is otherwise dubious. In particular, humans are unique in
that the female's breasts are voluminuous even when there is no child
to nurse. This unique adaptation has been explained by human
bipedality and frontal mating, unique among mammals, making it
advantageous to echo the age-old appeal of full buttocks with full
breasts. At puberty, the relative leg length of the female increases,
and this too is attractive to average males, though it is also
strictly adaptive.

Though large differences in heritable quality between two females
both of childbearing age easily overwhelm it, males clearly prefer females who exhibit the physical signs
of youth. These signs are present from adolescence to roughly age 27.
The physical robustness of youth is directly and dramatically
associated with the physical capability to succeed in pregnancy,
birthing, and rearing of young, and this wholly explains the male's
preference. Younger females are less likely to have sustained injury,
or to have contracted an infection or disease.

Sexually mature females preserve the characteristics of children to
a far greater degree than do sexually mature males. The chief
advantage of this adaptation was briefly mentioned above: the
potential for expressiveness is heightened, as is the prospect that
others will act toward them protectively (because treating them as
children). Some of these childlike characteristics attenuate
resistance to injury, but (as explored above in detail) they tend to
be beneficial overall. The male's sexual preference for young females
(who superficially resemble children) is sometimes distorted into a
pathological attraction to or preference for children as objects of
sexual attention.

Typical markers for the testosterone
suffusion that accompanies normal male puberty are a large chin, a
prominent brow, relatively sunken eyes, bushy eyebrows, dense facial
hair, deepened and strengthened voice, and amply proportioned
musculature, and these traits are attractive to average females. The
adaptive value of these traits is clear: they promote pugilistic,
industrial, and social robustness and effectiveness, and general
resistance to injury. Facial hair moreover tends to conceal injuries
- an asset in and of itself.

An intense preference for facial and body symmetry is common to
both genders. Somatic and cosmetic asymmetries record failures of an
organism to adhere to its genetically encoded body plan under
environmental stresses, and so tend to evidence counter-adaptive
genes.

Females, in contrast to males, have no particular age preference
per se. Instead, they prefer males who have demonstrated
exceptional leadership, survival, and productive capacities, and these
attributes tend to be evident in older males. Young males still exert
a particular attraction for females, however, because they have the
youthful physiological vigor with which to provide for the female's
physical requirements, and a psychological immaturity that facilitates
the bending of his will to her purposes.

Males are sexually stimulated by images of female genitalia, but
females are relatively unresponsive to images of male genitalia. This
dimorphism is explained by the differing roles of the two genders in
procreation. As noted above, mechanically the male plays the active
role, and the deliberation and cooperation of the female are not
necessary, only facilitative. Thus, whereas in males specific immediate action prompted
by the sight of the female genitalia is decisively adaptive, in
females it is not nearly so consequential, and so a similar instinct does
not develop clearly. Females are, however, sexually stimulated by
images of the faces of desirable males. This response adaptively
interlocks with the various mechanisms whereby the female modulates
her fertility (discussed above).

In the industrial and technological era, the non-dimorphic
preference for an athletic build and sun-tanned skin is enhanced
because these traits have become luxuries whose attainment is a
time-consuming distraction from the formulae of economy, and thus
whose display advertises the excess fitness of the individual. As
technology makes the supply of food regular and dependable for the
prosperous, the survival advantage of excess fat vanishes, so that
trimness becomes an advertisement of prosperity. With ``anorexia
nervosa'' and ``bulimia nervosa'' this trend is carried to the point
of pathology.

*

Contraceptive technologies radically alter the cost analysis of,
and distort the social dynamics associated with, sexual conduct. In
general, the balance of power is upset, tilting dramatically back
toward the female. The female's preference for security-enhancing
social institutions is reduced, since rape does not lead to pregnancy.
Notwithstanding the relative rarity of the measure, personal weapons
(particularly, handguns) are the preeminent contraceptive technology,
and prevent not only the pregnancy, but the rape act itself, reducing
the preference for security-enhancing (and freedom-impairing) social
institutions to the maximum degree.

The statistics of firearms
ownership and usage bear out the protective role envisioned by women
who arm themselves, and also attest to the
profound predisposition of females, noted above, to act through social
intermediaries (or, at least, in a socially constrained way) rather
than directly. The Gallup organization, in a poll conducted
in 2005, found that 47% of men report gun ownership, compared with
13% of women. Of those who did report gun ownership, 74% of women reported self-defense as a reason, compared with 63% of men, and women reported hunting and target
shooting as reasons at lower rates than did men.
Inge Anna Larish, writing in the University of Illinois Law Review
(“Why
Annie Can't Get Her Gun: A Feminist Perspective on the Second
Amendment”, 1996), notes that
“While violent crime against young males decreased from 1974 to 1987,
violent crime against women increased nearly fifty percent. Ninety
percent of the 4,693 women murdered in 1991 were slain by males (only
one out of eight males murdered in 1991 were slain by females) and
every fifteen seconds a woman is battered.” That women have
more to gain from gun ownership than do men is clear, and that gun
ownership is much less prevalent among women than men is equally
clear. This game-theoretic disparity is probably explained at least
in part by phylogenetic predisposition, and the inability of phylogeny
to accommodate the rapid, fundamental changes of circumstance brought
about by technological innovation.

With medical contraception (through pharmaceuticals, mechanical
apparatus, surgical procedures creating temporary sterility, and
abortion), the female is able to deftly manipulate her fertility, so
that she chooses the occasion of impregnation (if any), and the father
of her children, with great precision and with no necessary regard for
her cohabitative partner. This is clearly important, though it is
simply a quantitative enhancement of an important phylogenetic
process. Medical contraception, because it is predicated on the
continued availability of complex technological products and services,
reduces the female's preference for security-enhancing social
institutions to a far lesser degree than do personal weapons.

All contraceptive technologies have a similar impact on the
procreative dynamic. Consider this parallel: if an appointment by a
person (in a bureaucracy) is ``sticky'' - can't be revoked absent
impeachable conduct by the appointee - then the appointer will make
his choice carefully and thoughtfully (at least comparatively). If
the appointer can revoke an appointment at any time, for any reason or
no reason, he will tend to make sloppy appointments, under the ``let's
give it a shot'' principle. In the former case, there is a
recognition of investment and concomitant careful attention, while in
the latter there is no sense of investment. The trouble is that the
latter system promotes neglect. Since repair requires action - the
revocation of an appointment - the tendency is to under-repair, and so
the bureaucracy steadily decays as it is populated by a steady stream
of slipshod appointments.

The parallel of the above to the instant biological dynamic may be
obvious. If a woman has no sense that a sexual partnership is likely
to constitute a procreative investment, she will be less
discriminating in choosing her partners. However, the very acts at
issue produce psychological attachments that tend to lead to actual
procreation, as the female deliberately removes the contraceptive
technology (typically after the couple has wedded). But the
relatively unfit partner has snuck past the female's discriminatory
sentry. In a natural setting, he never would have been allowed to be
intimate in the first place, and so the attachment, wedding, and
procreation, would never have occured. The forward-going result is a
tendency toward lowered fitness.

The female is able to use sex as bait, with no significant
metabolic consequence to herself (except that abortion, if this is the
chosen means of contraception, is moderately risky and injurious).
Using this tactic, females can create Skinner boxes that reward
compliant behavior in a lengthy campaign. By introducing noise into
the system (imperfect consistency in the reward signal) the
indoctrination of the male is made most effective.

STDs exert a pressure on the system approximately opposite that of
contraceptive technologies. A contraceptive technique or suite of
techniques that is both covert and provides confident protection
against STDs maximizes the influence of the phenomena described
above.

Absent immunity to STDs, sexual activity is associated with
important costs and risks for the female, remotely similar to but
hardly interchangeable with the investment dynamic of procreation
itself. The discriminatory principles at work are quite
different.

With investment by procreation, the forward-going fitness of the
partner is a paramount determiner, both because this fitness will tend
to be propagated to the children, and because this fitness will allow
the partner to effectively provide for the needs of the female and her
children.

Absent procreation, but present the risk of STD infection, the
discrimination includes no such longitudinal strategy. Determining
whether a prospective partner is infected is itself a cost, and the
requirement definitely tends to make the female less profligate, but
the selection of partners will nonetheless be less sensical then in a
completely non-technological setting.

*

Mothers inherently tend more toward other-centeredness (tailoring
behavior for the benefit of another) than do males, or females who are
not mothers. The latter evidently tend toward self-centeredness.
Self-centeredness is so strategically valuable that it is often not
abandoned unless and until other-centeredness is a clear imperative -
that is, until a child's survival is predicated directly on the
other-centeredness of its mother. Also consider that pregnancy itself
is an arrangement in which the female is parasitized by a separate, if
congenetic, organism. Also consider the modern institutions of
adoption and surrogate motherhood, in which the instincts formed to
benefit congenetic children are co-opted. The phylogenetic
predisposition toward potential other-centeredness is clearly greater
in females.

Note carefully that, in the final analysis, the other-centeredness of
mothers is just as self-interested as the self-centeredness of others.
It is simply that, by the action of certain brain organs, the reward
for (pleasure from) the other-centered behavior of provision and
protection, and the punishment for (pain from) failing in this
behavior, overwhelms other reward and punishment signals.

For the most part, males are subject to no emotions of protective
attachment with the robustness and intensity of a female's for her
children. In the environment in which human nature was sculpted by
evolution, there was no reliable method by which a male could
determine that a child is his own, while a female could not help but
know with certainty. In particular, there was a good chance that a
male acting to protect a child would reinforce genes that originated
with another male, actually inhibiting his own genes. Thus, the
male's protective instincts toward a child have far less intensity
than the female's - though of course they are still present, both
because the child might be his or at least carry some of his genes,
and because protecting the child protects the mother and gains her
allegiance. In a clear adaptation to encourage protective involvement
of the father, infant children bear a marked resemblance to the father
- and not to the mother - regardless of the child's gender.
An involved father is clearly a great strategic asset.

Human females, in an arrangement humans share with few other
species (with certain higher primates and whales, and perhaps a few
other mammals), often (and in modern times, almost invariably) live
many years into menopause. Because rearing of human
children is a lengthy and intensive process, childbirth made even more
perilous by advanced age imminently risks leaving existing children
motherless and so likely doomed. Moreover, procreation by a mother so
advanced in age that she is unlikely to survive long enough to
rear the new child, is futile.

A more complex dividend of menopause is the expected benefit of
cultural continuity imposed by these females on their family and
community, which at a certain age outweighs the expected benefit of
additional direct procreation. Of course, the communitarian and
domestic labor potential of the female is a simpler but similar
dividend, with a similar evolution in relative weight.

People undergo progressive stages of
mental petrification. The first stage accompanies the arrival of
sexual maturity and is not very constraining. In the female, a second
stage accompanies the onset of motherhood - this stage is due entirely
to relative invigoration of the amygdala and closely related basal
forebrain structures, raising the proportion of
thought and behavior due to its actions. A third stage accompanies
the onset of menopause.
The value system of a female at the onset of
menopause is almost certainly the value system the female will have
until the arrival of death. The menopausal female is essentially
incapable of changing major established values. The memory
coordination system (c.f. The Symphonic
Architecture of Mind) no longer coordinates broad persistent
changes to plastic neural substrate, so that even when a persistent
change of mind is consciously and clearly intended, the change tends
not to occur. Through psychopharmacology, this petrification could
probably be at least partially dissolved. Comparison between male and
female mental petrification is difficult, because specialization - a
male tendency - is a form of mental petrification that sets in early,
but is not a neurophysiological constraint (changes of specialty are
neurophysiologically feasible).

Among the above catalogue of mental dimorphisms a few have
neurophysiological correlates in portions of the brain that are not
dedicated to the mediation and projection of emotion. In particular,
the traditionally recognized male aptitude for spatial cognition, and
female aptitude for symbolic cognition - if indeed real at all (I am
personally skeptical) - would have correlates in such non-emotional
regions. The dimorphism in the form of aptitude (with vs. without a
social intermediary) for pursuit of goals also must have such
correlates. The dimorphism in the tendency toward specialization also
must have such correlates. The staged petrification of the female
mind is also a phenomenon implicating non-emotional regions of the
brain. However, the great bulk of the dimorphism is embodied by the
emotional organs of the basal forebrain - mostly, the amygdala. (In
this paper, for the sake of cogent brevity I have omitted the
correlations between behavioral dimorphisms and the nuclei of the
hypothalamus.)

The amygdala is about the size of an almond, and is positioned just
inside the brain's front surface, low within the anterior part of the temporal lobe. It is a
heuristic engine that, largely by hereditary predisposition, models
natural physical principles, particularly in terms of competition and
cooperation, and generally by creating pressure to behave in a manner
the amygdala adjudicates is conducive to long term (hereditary)
biological survival.

The amygdala is the tyrant dictating the emotions described above.
A brief examination of the overall pattern of this tyranny reveals
that it is dimorphic in its overall influence. Female cognition, at
least after attainment of sexual maturity, is more tightly constrained
by amygdalar tyranny, than is male cognition. A very precise and
conservatively planned behavioral dance is required of females, if the
community is to increase (or at least maintain) its numbers. The
amygdala patiently and relentlessly walks the female through these
steps.

Males are subject to less mental predestination in general, and
less amygdalar tyranny in particular, precisely because there is such
an advantage in a thorough exploration of the range of possible
individuals (and concomitant fitness) made feasible by the greatly
reduced sensitivity of the population to failure by males. The
mammalian brain outside the basal forebrain has such plasticity that the
same genotype can lead, through divergent experience, to personalities
(goals and values, cognitive aptitudes, habits, etc.) that are
radically divergent. This free formation of personality is a gamble,
one that - viewed from the perspective of game theory and system dynamics - makes far
more sense for males than for females. Evolutionary pressure thus
allows the female mind less freedom.

It is important to recognize that the amygdala's actions (and those
of the hypothalamus) are not strictly reasonable, and are certainly
not the product of the sort of explicit reasoning consciousness
performs. All of the basal forebrain's actions can in principle be explained, of
course, but they are driven by crude phylogenetic heuristic models
that are prone to important errors of detail. Mature females, in whom the
balance of power is on average tilted toward the basal forebrain (and
away from the potentially conscious reasoning mind) more than it is in males, are
likely thus more prone to carrying into action certain errant commands of the basal
forebrain. Mature females are also less able than males to detect
that a thought or preference is amygdalar in origin, since the
amygdala is more entrenched by influential connectivity with the
machinery of literate cognition (in females only, significantly lateralized to the dominant
hemisphere).

I must stress this closing point: I know of no qualitative
dimorphism of the human machinery of cognition. Despite the array of
mental constraints enumerated above, a given male or female can,
through mental discipline, perceive, cogitate, and act, quite
independent of these constraints. That said, any person, male or
female, will with some frequency encounter circumstances in which
these contraints influence or dictate perception, cogitation, and action. Through
discipline, an individual can make this the exception, rather than the
norm.

By Rachel Emma Silverman

Getty Images

Fathers often talk the talk about sharing parenting duties with mothers when it comes to a newborn. But a new study finds that couples who profess to believe in equally-shared parenting rarely do so in practice.

The researchers surveyed 181 married, heterosexual, tenure track professors with children under age two. All of the professors had access to paid parental leave. Each survey participant was asked how their handling of about 25 child-care tasks compared with their spouse's handling of the same tasks. Among the tasks: changing child's diapers; taking child to doctor; feeding the child; staying home from work to care for the child; giving child a bath. (See the full list on page 21 of the study.)

The majority of professors – both male and female, particularly the women – held the view that men and women should share child care duties. But only three of 109 male faculty members surveyed reported that they did half or more of the care, while 70 of 73 women reported doing at least half–even when both spouses worked full time.

The study found that female professors who take paid maternity leave spent most of their time off to focus on infant care, including breastfeeding. Male professors, on the other hand, used their paid paternity leaves to focus on things other than infant care, such as research and publishing papers.

The study also found that women enjoyed doing child care work more than men.

“Our results suggest that one reason why female professors do more child care may be that they like it more than men do,” the researchers wrote in the study. “This conclusion is possible even though the vast majority of female respondents and a clear majority of male respondents believe that husbands and wives should share child care equally. Gender ideology about care may be less important than feelings on these matters.”

The study, in the January issue of the Journal of Social, Evolutionary, and Cultural Psychology, was conducted by Steven Rhoads, a political scientist at the University of Virginia and his son, Christopher Rhoads, an assistant professor of education at the University of Connecticut. (One caveat: the survey of the professors was done in 2001 — and ideas about gender and parenting may have changed over the last decade.) (Our fellow WSJ blog, Ideas Market, also has a take on the research here.)

The researchers say that offering paid paternity leave might actually serve to advance men more than women because men tend to use the time for professional work. While only about 12% of men currently utilize their post-birth leave option, the study finds, “if men should begin to take leave in much larger numbers, far from leveling the playing field, gender-neutral, post-birth leaves are likely to tilt the field further in favor of men.”

One could also argue, though, that paternity leave offers men the opportunity to learn to do more at-home and child-care tasks — and true equality in the workplace will never occur unless there is home equality as well.

Readers, what’s your take: Is paternity leave just a free ticket for dads to advance their careers? Male readers, how did you spend your time if you took paternity leave? Check out this list of child-care tasks on p. 21 of the study. Who does more of the tasks in your family? And who enjoys them more?

Does Survival of the Sexiest Explain Civilization?

Evolution by sexual selection is an idea that goes back to Charles Darwin. He had little doubt that it explained much about human beings, and modern biologists generally agree. One of them has even put a figure on it, concluding that some 54.8% of selection in human beings is effectively caused by reproduction of the sexiest rather than survival of the fittest.

Some years ago, the evolutionary psychologist Geoffrey Miller in his book "The Mating Mind" explored the notion that since human males woo their mates with art, poetry, music and humor, as well as with brawn, much of the expansion of our brain may have been sexually selected.

Recently Jason Collins and two colleagues at the University of Western Australia, in a discussion paper posted on the Web, have made the case that sexual selection explains civilization itself. They mathematically explored the possibility that "as females prefer males who conspicuously consume, an increasing proportion of males engage in innovation, labor and other productive activities in order to engage in conspicuous consumption. These activities contribute to technological progress and economic growth."

Psychological evidence points the same way. In one experiment, men who were shown pictures of women promptly expressed more extravagant desires for expensive luxuries, whereas women showed no such effect after seeing pictures of men. There's historical evidence, too. As Aristotle Onassis is supposed to have said, "If women did not exist, all the money in the world would have no meaning."

Moreover, Michael Shermer, in his book "The Mind of the Market," argues that you can trace anticapitalist egalitarianism to sexual selection. Back in the hunter-gatherer Paleolithic, inequality had reproductive consequences. The successful hunter, providing valuable protein for females, got a lot more mating opportunities than the unsuccessful. So it's possible that men still walk around with a relatively simple equation in their brains, namely that relative success at obtaining assets results in more sexual adventures and more grandchildren.

If so, this might explain why it is relative, rather than absolute, inequality that matters so much to people today. In modern Western society, when even relatively poor people have access to transport, refrigeration, entertainment, shoes and plentiful food, you might expect that inequality would be less resented than a century ago—when none of those things might come within the reach of a poor person. What does it matter if there are people who can afford private jets and designer dresses?

But clearly that isn't how people think. They resent inequality in luxuries just as much if not more than inequality in necessities. They dislike (and envy) conspicuous consumption, even if it impinges on them not at all. What hurts is not that somebody is rich, but that he is richer.

This is a classic statement of sexual selection. It isn't the peacock with the big-enough tail that gets to mate; it's the peacock with the biggest tail. If this sounds old-fashioned in an age of working women, gender equality and relative sexual continence, then open your eyes and look around you: The man with the most money or power still gets more sexual opportunities than the man with the least. Ask David Petraeus.

In human beings, females compete for males as well as vice versa. In many species, sexual selection is a force that acts on only one sex, usually the male. Peahens, which can share the best males and don't require them to be diligent parents after mating, do not grow colorful tails. But in other species, notably some seabirds and parrots, where males and females share parenting duties equally, both sexes are equally colorful—a result of competition by both sexes to attract the best mates.